SMEIs are commercially available and are used to indicate the exhaustion of carbon beds and carbon absorbers. Conventional SMEIs, commonly known as sample stream breakthrough detectors, saturation indicators or breakthrough indicators are basically constructed from a hollow clear plastic cylinder, sometimes perforated on the sides, filled with granular colorimetric indicator, capped and diffusion-vented at both ends. In operation, these devices are connected to the outlet of sorbent media devices and changes color when the sorbent media is exhausted.
A major functional drawback of the known art is the false indication of the exhaustion of the sorbent media. This occurs because the colorimetric indicator is directly exposed to the outside environment; therefore any fluid contaminant that exists in the surrounding ambient atmosphere would change the color of the indicator before the exhaustion of the sorbent media, hence producing false positive result. High humidity causes the same problem.
Another major drawback of the current devices is the deterioration of the colorimetric indicator due to light exposure. This problem also produces a false positive indication of the exhaustion of the sorbent media because the light deterioration causes color change similar to the color change due to exposure to fluid contaminants. To overcome this problem, some manufacturers cover the device with a metal or opaque plastic lid. This solution solves the problem of the deterioration of the colorimetric indicator. However, in operation, the user should frequently lift the protective lid to see whether or not there is a color change in the indicator. This is causes significant distraction to the user, especially in a workplace environment.
Another functional problem associated with the current SMEIs is their low sensitivity to targeted fluid contaminants. The hollow clear cylinder is filled with the granular colorimetric indicator in an effort to slow down the deterioration of the indicator due to light and humidity. However, the high capacity of the indicator requires larger quantities of the targeted contaminant to cause noticeable color change, hence causing a false negative result.
Accordingly, a need has risen for an SMEI with no false positive or false negative indication of the exhaustion of the sorbent media that is highly sensitive to toxic contaminant fluids and that operates independently of the surrounding environment, whether it is toxic contaminant fluids in the ambient atmosphere or the light condition.
A search of the prior art did not disclose any patents that read directly on the claims of the present invention; however, the following references were considered related.
Philip; (U.S. Pat. No. 2,951,156) reported that the residual life of carbon adsorption beds can be determined by passing beta-radiation through the adsorption bed.
Thomas; (U.S. Pat. No. 7,744,684) claims high capacity gas filter system, having a visible indicator showing when the filter is spent.
Arno, Michael J.; (U.S. Pat. No. 7,285,156) claims a dryness indicators designed to visually indicate the moisture content of compressed gas or air delivered to a point of use.
There are also numerous literature and patents on end of service life indicators (ESLI) for respiratory cartridges. These devices, generally, comprises a sensor (colorimetric or electronic) imbedded inside the respiratory cartridge and function to alert the user before the consumption of the sorbent media inside the respiratory cartridge.
The following patents and references therein disclose various respiratory cartridges and protective equipment with ESLI for alerting when the cartridge or the protective equipment is exhausted, thereby requiring replacement: Yablick M.; (U.S. Pat. Nos. 1,537,519 and 1,725,893), Wing R. E.; (U.S. Pat. No. 4,365,627), McAllister J. W.; (U.S. Pat. No. 4,155,358), Leichnitz K.; (U.S. Pat. No. 4,684,380), Curado L.; (U.S. Pat. No. 6,497,756 B1), May W.; (U.S. Pat. No. 5,297,544), Bernard P.; (U.S. Pat. No. 6,375,725), Attar; (U.S. Pat. No. 7,503,962), Kirollos; (U.S. Pat. No. 7,927,558). In all the above mentioned devices, to apply an ESLI to a filter or a respiratory cartridge, major modifications should be done to the filter or the respiratory cartridge to accommodate the ESLI. In case of colorimetric ESLI, the filter or the respiratory cartridge housing should be at least partly clear to allow user to observe color change. The indicator should be placed inside the filter or respiratory cartridge in such manner that will not obstruct fluid flow through the filter or respiratory cartridge or causing channeling that deem the device ineffective. Further, filters and respiratory cartridges by themselves have no shelf-live. Inserting an ESLI into filters or respiratory cartridges during the manufacturing process require manufacturers to provide shelf-live date or use-before date, after which the device cannot be used. This limitation causes major logistic and inventory control burden for both manufacturers and end users.